osd/osd_type: Befroe call rebuild() check the is_contiguous().

The aim of trim_bl() is make a contiguous ptr. Before call rebuild()
first check whether contiguous.
Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
bufferlist: Don't call rebuild(), c_strt() call it  if bufferlist not
contiguous.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>